The present invention relates to a metal-air battery-powered electric vehicle.
More particularly, the present invention relates to such a vehicle having a collision safety device incorporated therein.
Various proposals have been made in the past for electric-powered vehicles. To date, for a number of reasons, electric vehicle systems have yet to become commercially viable for urban and highway applications. There have been proposals to employ zinc-air batteries for urban vehicle propulsion. An example is the publication "Improved Slurry Zinc-Air Systems as Batteries for Urban Vehicle Propulsion, " by P. C. Foller, Journal of Applied Electrochemistry, Vol. 16, pp. 527-543 (1986).
Metal-air battery structures are described in the following publications: U.S. Pat. No. 4,842,962, entitled "Zinc Electrode and Rechargeable Zinc-Air Battery;" U.S. Pat. No. 4,147,839, entitled "Electrochemical Cell with Stirred Slurry;" U.S. Pat. No. 4,908,281, entitled "Metal-Air Battery with Recirculating Electrolyte;" U.S. Pat. No. 3,847,671, entitled "Hydraulically-Refuelable Metal-Gas Depolarized Battery System;" U.S. Pat. No. 4,925,744, entitled "Primary Aluminum-Air Battery;" U.S. Pat. No. 3,716,413, entitled "Rechargeable Electrochemical Power Supply;" U.S. Pat. No. 4,925,744, entitled "Primary Aluminum-Air Battery."
One of the characteristics of metal-air batteries such as zinc-air is that, unlike conventional batteries such as lead-acid and nickel cadmium, in which both the anodic and cathodic active materials must be stored within the plates of the cell, in metal-air only the anodic active material (the zinc in the case of zinc-air) is stored within the system. The cathodic reactant (oxygen from the air) is supplied from outside the battery from the surrounding air, either by natural diffusion in the case of small size, low power, single-cell units, or by forced flow (from, for example, a fan or blower) in the case of large size, high power, multi-cell assemblies. A typical example of the former category is a zinc-air button cell for a hearing aid, relying only on natural diffusion of air, and able to supply a current density only in the range of 1-10 mA/cm.sup.2. A typical example of the latter category is a zinc-air electric vehicle battery, comprising close stacking of perhaps as many as 400 cells, requiring an air blower, but capable of supplying continuous current density of the order of 100 mA/cm.sup.2 and peak current densities of 400 mA/cm.sup.2.
Particularly for the latter application, high power batteries for electric vehicles, an important consideration is the system safety under accident conditions (e.g., collision). Simple electrical disconnection of the load (i.e., the electric vehicle motor) from the battery in the case of a collision is certainly advantageous, since the battery and motor are returned to a non-active state, now being isolated and inoperative. A problem can arise, however, if component cells of the battery are damaged, for example, if battery plates with opposite polarity are distorted by the collision and touch, forming a short circuit. Isolating the battery from the motor will not help here, since individual cells or groups of cells could still provide high levels of local current and local heating, perhaps involving the risk of fire. This is especially the case with batteries of the conventional kind, wherein plates of opposite polarity are carriers of their own respective active material masses, and individual shorts could still continue damage scenarios after the collision. Even in the case of a metal-air battery such as zinc-air, where only the zinc anode material is carried within the battery, as long as the air supply is continued to the cells, subsequent damage can be sustained in individual shorted cells or groups of cells.
In U.S. Pat. Nos. 3,743,849 and 5,327,990, there are disclosed apparatus for automatically disconnecting the power circuit for vehicles during impact and which also shut off the fuel supply to the motor; however, said patents are addressed to the inactivating of internal combustion engines and do not teach or suggest an appropriate solution for electric vehicles.
In U.S. Pat. No. 5,238,083 this problem is dealt with in electric vehicles by providing an impact sensor connected to a controller for changing the battery units from a connected state to a state separated into a plurality of groups.
This solution is impractical, however, for electric batteries now proposed for electric vehicles, wherein the battery is composed of several hundred interconnected cells.